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JEE Advanced 2022 Paper 2 · Mathematics · Area Under Curves · medium

The area of the region bounded by the curve y=lvert x^2-4rvert and the line y=5 is

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The area of the region bounded by the curve y=∣x2−4∣y=\lvert x^{2}-4\rvert and the line y=5y=5 is
  1. A. 443\dfrac{44}{3}
  2. B. 3636
  3. C. 403\dfrac{40}{3}
  4. D. 523\dfrac{52}{3}
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Answer: (A) 443\dfrac{44}{3}

The line meets the curve where ∣x2−4∣=5|x^2-4|=5. Since x2−4=−5x^2-4=-5 has no real solution, the only intersections are x2=9x^2=9, i.e. x=±3x=\pm3. The region is symmetric about the yy-axis, so area =2∫03(5−∣x2−4∣)dx=2\int_0^3\bigl(5-|x^2-4|\bigr)dx. On [0,2][0,2], ∣x2−4∣=4−x2|x^2-4|=4-x^2, so the integrand is 1+x21+x^2 and ∫02(1+x2)dx=2+83=143\int_0^2(1+x^2)dx=2+\frac83=\frac{14}3. On [2,3][2,3], ∣x2−4∣=x2−4|x^2-4|=x^2-4, so the integrand is 9−x29-x^2 and ∫23(9−x2)dx=9−193=83\int_2^3(9-x^2)dx=9-\frac{19}3=\frac83. Hence the area is 2(143+83)=4432\left(\frac{14}3+\frac83\right)=\frac{44}3. The value 3636 results from ignoring the modulus and integrating 9−x29-x^2 over [−3,3][-3,3].
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